adding another hot water tank

ok this is probably an odd question on here but here goes i live in an rv so adding a larger hot water tank isnt really an option 10 gallon is as big as they come so i was wondering if i could put another tank right next to it and hook it up in a series for more hot water because 10 gallons just dosnt last verry long when showering at all

If the tank is well insulated, and the thermostat can be cranked way up, it's probably cheaper/more space-efficient to install a tempering valve at the output (set to 120-130F) and bump the tank temp up to 140-150F. If the insulation on the existing tank isn't so great the standby losses will go up considerably though.

Otherwise, putting them in series is fine for additional capacity, putting them in parallel (with carefully plumbed symmetry) will improve flow. All else being equal the standby losses of 2 tanks will be more than a single tank of equivalent volume (imagine that! ), and probably more than a single well-insulated tank running at higher temp with tempering valve on the output. If there's space for a 15-18 gallon tank it's probably better from an efficiency point of view to replace the existing tank with the biggest tank that fits and add a tempering valve at the same time "just in case", then tweak up the temp only as much as is necessary for showering.

OTOH, (as owners of tankless HW heaters know), the definition of how long a decent shower is can grow to meet the new improved capacity. ;-) (I've heard of one guy who put a timer switch on the power to his tankless to keep his teenagers from taking hour-long showers. ;-) )

yea thats the problem with rv tanks non adjustable you only get 1 temp...... the problem with a larger tank is the way an rv is set up it would not fit thease tanks sit on their sides also i would need the ability to heat on gas or electric like already as far as flow goes rv piping is only raited for 55-60 psi have to have a regulater on most of the time ne way so water pressure is never good just looking for more then five mon of hot water as far as recovery goes no big deal just me any way i only take 1 shower a day on most days any way

yea thats the problem with rv tanks non adjustable you only get 1 temp...... the problem with a larger tank is the way an rv is set up it would not fit thease tanks sit on their sides also i would need the ability to heat on gas or electric like already as far as flow goes rv piping is only raited for 55-60 psi have to have a regulater on most of the time ne way so water pressure is never good just looking for more then five mon of hot water as far as recovery goes no big deal just me any way i only take 1 shower a day on most days any way

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Bummer!

I'm not very familiar with the RV-specific issues- is there a way to plumb in something to be able to use a cheap black-plastic batch solar HW heater on the roof in series with the heater's input, to use as a tempering tank in warmer/sunnier weather, at least? (It should improve recovery times, or even provide a reasonable amount of afternoon HW on any sunny not-so-chilled day.)